All users have a limited memory space. There is a moment at which this magical boarder is reached and you have to clear up your space.
If you aren't able anymore to log in on the terminals you can use the ssh-connection on clienssh1.rbg.informatik.tu-darmstadt.de or clientssh2.rbg.informatik.tu-darmstadt.de - there is the login still possible (as long as the account is not blocked).
To display which subdirectory contains large files the command tell-me-disk-usage and as alternative the following longer command:
find -print0 -mindepth 1 -maxdepth 1 | xargs -0 du -ks | sort -n
find . -maxdepth 1 -type d -exec du -hs {} \;
The command find is looking for all files and folders but only in depth one. xargs now executes the command Sie, which stands for »disc usage«, on the found data. As last step everything will be sorted by size by the command sort.
There are some files and directories which normally take the most space in the memory. Here are some names of directories that take a lot of space really fast (you can display them e.g. with ls -lal):
If you want to empty your home folder in total, because you stored your data or because you don't ned them anymore, you can find a tutorial for that on the the page on reseting the home directory.